Rotate two points on f-curve by opposite amounts
Can be done in 2 ways:

Selecting the first side inner handle and rotating it, then selecting the other side inner handle and pressing Shift+R to repeat the last rotation. Before doing anything else, press F9(F6 in blender 2.79) to open the options window. In that window you get the currently used angle, which if negativ needs to be made positive to mirror the rotation. Else other way around.

See in the little visual explanation:



The other way is by indirectly rotating through moving the handles:

You select the one side inner handle and press G followed by Y and move the handle to obtain the angle you want. After that you select the other sides inner handle and press Shift+R to repeat the movement, resulting in the exact same angle just mirrored. While rotation can also be repeated, it would be in the same direction and not result in a mirrored effect.

Little visual explanation: